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Why autogyros use pusher-, whereas, piston-engined planes use puller-configuration?
I found that most modern gyrocopters use a pusher-configuration, whereas, most piston-engined planes use puller-configuration.
Since the pusher-configuration has major disadvantages, are there specific advantages for autogyros?
Visibility is a positive effect of pushers, but this would also count for normal planes.

Pitcairn PCA-2 - By NASA/NACA, LARC [Public domain], via Wikimedia Commons
The original autogyros were tractor (google Cierva/Pitcairn).
The big thing with autogyros is thrust line relative to the vertical C.G.   The pusher craze was started by Igor Bensen with his homebuilt autogyro, which was done that way to keep everything compact and minimalist, and give the pilot a nice view.  The issue with Benson machines and variants is the thrust line is above the center of mass, and if you unload the rotor disc by doing a bunt, or hit major turbulence that makes you go zero G, they have a tendency to pitch over and tumble as the prop wants to spin the machine about its vertical CG in the absence of any resisting force.  It's called Power Push Over or PPO and is always fatal.  You must NEVER go zero G in a Benson or any machine with a high thrust line.  It's actually quite similar to the mast bumping problem with teetering rotor helicopters, although that happens on the roll axis.
A lot of gyros move the engine down as much as possible to lower the trust line to the vertical C.G. or close to it, and have that awkward spindly look as a result because it means making the gear a lot longer.  The other thing that helps is a large horizontal stabilizer to resist large pitching movements and most gyros have them now.
Tractor engine gyros have a better thrust line relationship (generally naturally lower, close to the CG) and also have a long tail with good moment arm and are generally immune to PPO (the fact that the engine is out front or behind is irrelevant in itself).  There are a couple of homebuilt gyros that use the engine out front.  You can tell however that the tractor machines just have way more structure to them so it's easy to see why the pusher setup is so much simpler and lighter.


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What is the meaing of the circuit breaker marking "Audio/Mkr" in a PA-28-181?
On the PA-28-181 that I fly, there's a circuit breaker called Audio/Mkr. What is that? In the aircraft, there's also a dual GNS430 if that makes it any more specific. I was thinking it could be controlling the speaker on the aircraft?

The electrical diagram in your POH should identify exactly the equipment plugged into that breaker if it was from the factory. What year PA28 do you have? They weren't great with manuals in the early years...

This circuit breaker is responsible for your Audio Control Panel. It's called Audio/Mkr. because the Audio Control Panel in most aircraft includes the Marker receiver and displays (maybe you noticed the three colored lamps on the left side reading O, I and M, colored white, blue and orange).
If the circuit breaker is out you loose your audio on the one hand side, on the other side you also loose your ability to identify Marker Beacons (functionality explained by Carlo).

It's the circuit breaker, most likely, for power from the avionics master bus to the audio panel as well as the marker beacon receiver.

What's a marker beacon receiver?

The marker beacon receiver used to be used for ILS approaches as a position cross-check, now it's essentially obsolete. Often built into the audio panel.

@nyorkr23 Marker beacons were (are) low power transmitters that transmitted a signal that causes a marker beacon receiver to beep as you pass over it. There were outer markers, middle markers, and inner markers in the order of their positioning along the ILS approach path, each marker transmitting beeping of a different sound and rapidity. There were a lot more outer marker installations than middle, and a lot more middle than inner. ILS installations that had all 3 were relatively rare. I encourage you to post your comment question as a regular question for a more detailed answer.

@nyorkr23 Here's a link to the Garmin GMA 340 Audio panel/marker beacon receiver.  You should have something similar at the top of your radio stack.

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How long does it take for a regular size airliner jet engine to be warm?
How long does it take from starting of turbine or turbofan or turboprop, either by using an APU or other methods, until the engine is warm enough for safely extracting full power for takeoff?

What is a "regular size airline jet engine"?

I mean something used for commercial flights, but not that small as a private or business jet. Thanks

Right, but what do you consider "regular"? The engines on the Embraer ERJ/CRJ? 737? 747? A320?

Standard, average, median size is a definition precise enough? An Airbus, any twin-engined passenger or cargo airplane, not an A380, This is not mathematics, but if you need stratifying response according to class, maker, power, or seats, please feel free to do it, even in the road

A320 with IAE engines has one of the longest shafts in business, and thus is most sensitive to temperature variations/deformations.
Don’t know what the producer requires, but operator procedure is 5 minutes from start to take-off power if the engine was shut down for more than 2 hours before.
Interestlingly enough, this is on top of other temperature limitations (eg min oil temp) and is the same time, regardless of outside temperature ( eg oil on cold day may take longer to warm up)

The P&W engines like the JT-3, JT-8, JT-9 are usually above minimum T.O. temperature by the time the After Start Checklist is completed. Initially, oil pressures can be on the high side in very cold weather but will quickly come down as the oil gets warmer. I have never had a T.O. delay due to engine temperature or pressure restriction with these engines. This was definitely not the case with the large radial engines when we had to have at least 40 deg. of oil temperature before the throttles could be moved above 1000 RPM to protect the engine and this could take several minutes. The large Russian aircraft like the IL-76 also play this warm-up game. The turbine blades in these engines are made of lower quality material than that of their American counterparts. They require warming up the engines in stages which involves several increases in power corresponding to increases in temperatures until such time as take-off power can be accepted by the engine without turbine or shaft failure. The procedure usually takes 10 to 15 minutes an a cold day.

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Could a tilt quadcopter use turbofan engines?
I was wondering whether having a quad tiltrotor would allow for the use of turbofan engine rather than turbo prop. I read on another question that the V-22 uses turbo prop as it is easier to balance, but if there were 4 turbofans then it could surely balance and with the engines closer. Could a turbofan tilt rotor be possible for supersonic speeds and VTOL? And would tilt rotor or tilt wing be better in this application? Also wouldn't turbo fan mean there isn't the stream to worry about between sets of motors?

I don't think its a limitation of turboprop vs turbofan, but rather redundancy. The V-22 can still fly if one engine fails because it has a gearbox that connects the two engines, so the good engine can power the bad prop. This would be a little difficult with a turbofan engine since (most) of the thrust is generated via combustion gasses rather than the propeller.

In a way, this has been done already half a century ago.
When NATO decided to try a VTOL strategy, the Harrier was not the only result. There was even a supersonic VTOL fighter, and it used swivelling engine pods at its wingtips, much like the V-22 does today. It was the VJ-101C, developed in Germany and first flown in 1963.

VJ-101C in flight. Note the opened intake door aft of the cockpit where two additional lift engines were complementing the thrust from the wingtip engines (picture source)
While the VJ-101C used six Rolls-Royce RB145 turbojets, a later production version was planned to use turbofan engines. NATO changed it's mind before the turbofan-powered version was built, however.

6 engines? In a fighter? I wonder why this didn't make it to production... /sarcasm. So, I see one at each wingtip, and two in the hatch behind the pilot. Where are the other 2 hidden? Are there actually 2 at each wingtip?

@FreeMan: Yes, the engines were spread in pairs over three points. How many legs must a stool at least have so it does not topple over? Right, three! And pairs were chosen for redundancy. Six was actually the smallest sensible number here!

Was the redundancy good enough to keep it flying if an engine failed on vertical take-off? The thing had insane amount of thrust, but according to the listed performance, one engine would still be a bit short of being able to hold its third of the weight and in hover the other engines can't help, because the thrust distribution is important.

@JanHudec: Not for a fully loaded plane, but for one at the end of its mission. An engine failure right after vertical liftoff with mass close to the limit would had resulted in an ejection and a wrecked plane.

@Peter kämpf if 3 is needed like a stool then how does the v22 do it?

@SRawes: With cyclic blade pitch adjustments, like helicopters do.

Well, I bet in filight you could use the secondary engines to power electronics.

The main reason V-22 uses propellers is efficiency. To get high thrust for power, you need to affect a lot of air and that requires a large propeller. The V-22 has huge propellers, closer to helicopter rotors than typical aircraft propellers. This gives it the static thrust-to-weight ratio of more than 2, so even with one engine out it still has more than 1 and can keep hovering.
At higher speeds, propellers loose their advantage as they don't work well at high speeds, so for transsonic turbofans become better and as the speed increases further, you need to reduce the bypass ratio. But since jets have relatively low static thrust, a jet VTOL needs a really powerful engine.
Now, they can be made. F-35B is a supersonic VTOL and does it with just 1 engine. The engine needs to be really huge for the aircraft (which is the case for all fighters, but not other aircraft classes), but it still gives a static thrust-to-weight ratio of around 1 (F-35B can't do pure vertical take-off at MTOW). There is no way to install two such engines on the plane to get hover ability with one engine inoperative. And the fuel consumption is huge, which is acceptable for fighter, but would not be for transport aircraft.
Last, 4 engines would be actually much harder to balance than 1 that splits the air over multiple jets. This is because jet engines have significant lag in thrust command response and can't be controlled all that precisely. On quadcopters the electric motors respond immediately to control input and in large propeller/rotor aircraft the propeller/blade pitch is used which also gives immediate response, but jet engines need to match their rotational speed to power and that takes too much time. It is easier to split the flow from one engine using variable guide vanes.

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What are the advantages of a geared contrarotating turbofan?
I read that this would be the holy grail of jet engines:
Next Gen NB Engines : Contra Rotating Turbofan Fan
Why is this so and what problems are stopping us from doing this?

How is this different from the question you just asked? Contrarotating turbo fan fan

I was unsure whether there were advantages other than efficiency and why it being geared would make a difference, i thought you would want them to be equal speeds. The question i swhy are there these advantages and what difference being geared would have. @fooot

what problems are stopping us from doing this?

In some sense, it's business reasons. Developing a brand new jet engine from scratch costs a lot of money. Usually the pricetag runs into the billions. It will often take 10 years from the time you start to develop a new engine until you see a single dime of profit. If you are the board of directors of an engine manufacturer, and you give the greenlight to develop a new product, you might be literally betting the entire company on the success of that new product. So, you have a tendency to be conservative. If you can get a 10% performance improvement from some new never-tried-before fancy contra-rotating fan thingy, or you can get a 5% performance improvement by keeping the same basic tried-and-true design but just tweaking the aerodynamics a bit here and there, you are probably going to go with tried-and-true. Eventually, a limit will be reached where the basic turbofan architecture cannot be tweaked anymore, and then you may see some new thing like this tried, but I don't think we are quite there yet right now.


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Why do turbofan engines not have a contrarotating second fan?
Why aren't planetary gears used to have a fan in front of the fan in a turbo fan engine. Would this not lower energy consumption etc?

Related: Why are contra-rotating jet engines so rare?

I mean could you not have a double fan in a turbo fan going in opposite directions by using planetary gears. why isn't this done when contra-rotating propellers have advantages that I would guess are transferable to turbo fans. this seems like a simple way of doing it? @mins

It's not simple, in the same way that contra-rotating propellers are not simple and we don't see them very often.

The power to drive a fan through a gearbox is not beyond current technical capability. Pratt & Whitney have developed the geared turbofan, the PW1000G that first ran in 2008 and entered commercial use in 2016, flying on 4 different aircraft, including the Airbus A320neo. This enables the fan to spin at a slower speed than the low pressure turbine, such that the turbine spins at a higher speed that is more efficient for power extraction from the relatively high velocity mass flow, while the fan spins at a lower speed that avoids the blade tips lossing efficiency or creating noise at take-off, due to near sonic flow.
The engine design involves trade-offs. The complexity and weight of a counter rotating two stage fan needs to be balanced against the achievable pressure ratio with a single stage fan, and the added benefit a two stage fan would provide. Some design work has considered counter rotating compressors for example, this thesis. or even earlier work in  1992. The gas turbine industry can be quite conservative - it costs huge amounts of money, and time, to develop a new engine design, and radical steps are much less common than evolution. Pratt took a gamble, that appears to have paid off, though they do still have some issues. However, it took them decades, and around $10 billion. Rolls Royce are considering a similar design (the UltraFan), but GE are more wary. They have chosen the use of new materials as they felt the addition of the extra component would add reliability, weight, and durability challenges that they could avoid by using material improvements instead. For example, the use of ceramic matrix composites in the hot section of the CFM56 LEAP. They claim this gives 15% fuel savings, but has taken 25 years to develop. In comparison, P&W claim the GTF is 16% more fuel efficent than current generation engines. So each manufacturer choses the route they are comfortable in, and may get to the same end point.
In general, the desire has been to increase by-pass ratio, as this lowers specific fuel consumption. However, increasing BPR results in larger diameter fans, and higher tip speeds, approaching sonic velocity if the turbine is run at the optimum rpm. Hence, the geared fan approach. Clearly, Pratt & Whitney did the trade-off analysis, and decided this was the best approach for a geared fan, balancing techncial risk, reliability, performance, in-service cost, and weight.

Well, PW1000G is still just a medium engine. Nobody tried to make a geared turbofan of the size of Trent 900 yet.

Also, you didn't really touch on the difference between just geared turbofan, where the fan spins at different speed from turbine, and contra-rotating fans, where there would be two fan stages rotating at opposite directions. The relative speed would be greater and so there would be greater losses in the later case—with little benefit, because a stator is almost as good and much simpler.

@Jan.  Your comments are fair, Jan. It is more of a general answer, than really getting to the technical crux of the question.

The power needed to drive a large fan is currently beyond of what is technically possible in gearbox engineering. The swirl losses of a single-stage fan can be somewhat recouped by inclining the struts holding the fan fairing, so a contra-rotating fan is not much of a help, but a tremendous engineering challenge.

EDIT:
Clarification: Small geared fans do exist for a few decades already (Lycoming ALF502) and the maximum size of geared fans is increasing, but the size of the biggest engines is still far out of reach of today's technical possibilities. The biggest geared fan today has ⅓ of the thrust of large turbofans.

There is a reason why one might think counter-rotating fans could reduce energy consumption: any propeller or fan causes the air to move, besides the desired axial direction, also to some degree in a circular swirl manner. This is wasted energy.
There are different ways to reduce this loss. The simplest is to increase the diameter and decrease the blade angle of attack. But increasing the diameter can't be done without limits, and low AOA requires the blade tips to move faster – possibly supersonic, which creates its own problems. For this reasons, most big turboprops have relatively small, many-blade, relatively high AOA props – although that's not optimal swirl- and bladetip-vortex wise.
The most extreme approach is counter-rotation. A second coaxial propeller can cancel out the swirl, without increasing the diameter at all. So this is in particular useful for very large turboprop planes, the Tupolev TU-95 being the prime example. This plane still had supersonic prop-tips.
In a turbofan, the swirl is actually even more of an issue, because you have small diameter, lots of blades with a high angle of attack (and also high camber). But turbofans don't actively cancel that swirl, instead they use it passively to gain extra thrust. That does in fact not require contra-rotation, but only stator vanes. What these do is, they redirect the swirling motion backwards. That still recovers much of the energy loss from swirl, while being much less complex than gearing for counter-rotation would be.


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Do all the engines/propellers of a VTOL UAV need to be identical?
I would like to know if VTOL UAVs necessarily need $n$ identical propellers and motors. Have any design solutions considered the possibility of using non identical props? For instance 2 motors of type A, 2 motors of type B, and 2 motors of type C. If so, where can I find some studies or some designs that have attempted this kind of solution?

I was thinking of VTOL UAVs featuring many motors, say 6 or more. In these cases it may be useful to use under given conditions and maneavures to not use all the engines, as it may imply that the working point would not be close to the optimum. The things you are pointing out would certainly be the disadvantages of having such solutions. Yet for high performance UAVs it may still be more important to have better consumptions or efficiency than better costs. @mins

MIT CSAIL has researched apparently quite thoroughly on this and the end result it would seem is that you can have ANY different size of motors be able to fly given that it satisfies certain conditions such as thrustep etc. For this I would recommend following developments in two areas (as far as my knowledge goes)
First of ckurse MIT CSAIL's video demo of their custom software to simulate all combos of motor thrust and positioning

The next 'guy' you want to follow is ofcourse
Raffaello D'Andrea  and his research team. His TED talk explores drones at mechanical disadvantages, here you go
https://www.ted.com/talks/raffaello_d_andrea_meet_the_dazzling_flying_machines_of_the_future
That's as far as my enthusiast knowledge could help


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Would it be beneficial for the Boeing 777x to have a biplane wing design?
The Boeing 777x has huge wings to generate lift even to the point of having to have a hinge and being able to bend them.
Would it not be advantageous to have 2 wings like a biplane or one behind another? And what disadvantages would there be?

A biplane wing of a given span and chord has twice the area of a monoplane the same size and so can fly more slowly, or for a given flight speed can lift more weight. Alternatively, a biplane wing of the same area as a monoplane has lower span and chord, reducing the structural forces and allowing it to be lighter.

This is from Wikipedia so possibly not reliable.

I hope the wikipedia poster realises that biplanes are out of fashion for a reason.

I'm not sure if this is an exact dupe, but these two questions probably cover the essential information: here, here.

Why not combining stacked and successive, and use 3 instead of only 2, like this...

Not really what I had in mind. I was thinking a normal biplane (wing over wing) or wing and a second wing further back on the plane. @mins

A major disadvantage to that design would be the aft wing had a disrupted airflow over it as it travels through the fwd wing's wake, so lift is greatly diminished.
As to doing a stacked biplane design typical of small sport biplanes in use over the years, this is probably frowned upon for two reasons:

High Drag - more structure in the relative wind always means more drag anemic this was one of the major advantages to the cantilevered wing developed in the 1930s.
Heavier - more wings means more structure both in terms of the second wing itself plus the mounting structure to mate the wing to the fuselage.

A single cantilevered monoplane is by far the most efficient solution save only a flying wing, but these are not commonly used in commercial travel which has been discussed in previous threads.
Now that's not to say a biplane may not be useful for commercial aircraft.  Researchers at MIT proposed a supersonic biplane design which usea the configuration to dramatically reduce its sonic boom.

Whether this idea survives the CGI proposal and becomes actual hardware is another story; this business is full of concept aircraft and precious little flyable hardware.

For the biplane wouldn't it be equal drag as having 2 wings could be half the length of would they need to be more than half? Same for weight wouldn't you need half the length which would mean force isn't leveraged as shorter wing so lighter structure?

You also have to take into account, the mounting structure, increased flat plate area, form drag, etc from such a design.  It's not quite that simple.

@SRawes, the main reason why biplane would have more drag is the shorter span. The induced drag decreases with span and there is no way around that.

The Boeing 777x has huge wings to generate lift

No, Boeing 777x has long wings to be efficient.
Generating lift using a finite wing comes at a cost of induced drag and this decreases with wing span. While parasite drag increases with frontal area. The induced drag also decreases with speed, while parasite drag increases. Optimal performance is achieved at the point where induced and parasite drag are equal.
As the designers improve the aerodynamics to reduce the parasite drag, the optimal point¹ shifts to longer wing span as that decreases the induced drag, and increases parasite drag slightly so they are equal again.
So the B777x has the wing span that gives it optimal efficiency. No other wing shape would be able to provide that efficiency.

¹ Assuming the cruise speed should remain the same, M0.85 somewhere around FL360–FL400. Optimal wing span decreases with increasing cruise speed.


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Why hasn't Boeing updated the 747 with technology from the 787?
Why hasn't Boeing updated the 747 with technology/designs from the 787 Dreamliner? Surely this would be a very successful aircraft as it could have the best of both designs.
Has Boeing explained why? Are there any reasons this couldn't or shouldn't be done?

They did, in the 747-8:
Wikipedia:

Similar in nature to the 747X, the stretched 747 Advanced used technology from the Boeing 787 Dreamliner to modernize the design and its systems. On November 14, 2005, Boeing announced that it was launching the 747 Advanced as the "Boeing 747-8"

(Emphasis mine)
The 747-8 includes technology in the cockpit, cabin, wings, and engines borrowed or learned from the 787 and 777 aircraft programs. Obviously you can't just pull the wings off of a 787 and stick them on a 747, but the wings were redesigned with aerodynamic information learned in the 777/787 program.

Have they increased the window size and made them electronically dimming? Also is the cabin pressurised to a higher level, @RonBeyer

@SRawes Yes, the windows are larger, but I'm not sure if they are electronically dimming. If you want to read about the similarities between the 787 interior and the 747-8 interior, here is a good read with a video.

I think it really comes down to money, there isn't enough demand for planes in the 747 size category to justify a clean-sheet design with a composite fuselage.

The are not electronically dimming on the 747-8. But much bigger and that's a nice thing for passengers :)


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What is the difference between RNAV and RNP?
What is the difference between RNAV and RNP?  I know that RNAV doesn't need monitoring and alerting, but RNP does.

Related

I read it before . Won't help

Yeah, it doesn't answer your question. It's just related. RNP is really a subset of RNAV. Somebody will come along and write an answer for it. You can also check out this page

It is probably useful to understand that the term RNAV preceded GPS.  (by decades...)
Older electro mechanical inertial, and I think even LORAN based systems were RNAV capable, but you couldn't shoot a modern RNAV approach with one.  (presumably why most approaches are labeled "RNAV (GPS)"...)

RNP is a superset of RNAV requirements. It applies and communicates a performance specification for RNAV that may vary by location rather than by equipment.
On board performance monitoring in RNP requires an alert when the system cannot guarantee with sufficient integrity that position meets required accuracy. Required accuracy can vary. A tight approach may require 0.1nm accuracy while 5-10nm over oceans might be acceptable. RNP requires communication of a numeric qualifier for accuracy. RNAV has no such mechanism.
Confusion is understandable as the terms are sometimes used interchangeably. ICAO is arguing with FAA and other countries to rename RNAV approaches as RNP approaches. The ICAO position is more clear, the FAA position supports existing equipment and training. Everyone believes a navigation performance spec needs to be communicated to pilots in charts and equipment, but there is no clear answer as to how to do it at this point.

RNAV, or Area Navigation is a means of navigating that allows direct routing between any two points on the earth. This is opposed to VOR only navigation that requires following routes that pass along radials of the VORs. An FMS or GPS navigator are both RNAV capable systems.
An RNAV procedure is one that requires you to have an RNAV system in order to fly it.
RNP, or Required Navigation Performance adds specific performance standards onto RNAV systems. It defines several levels of performance that are applied to specific airspace and operations. The need for these levels is driven by airspace management and air traffic control (keeping planes from running into stuff or each other).
The most visible part of RNP is the monitoring and alerting requirements. An RNAV system can compute your aircraft position to some level of accuracy. With RNP the system must estimate its actual navigation performance (ANP) and compare it to the specified RNP for the airspace or operation you are flying. An alert is generated if the RNP is not being met.

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Are fighter jets vulnerable to .50 caliber gunfire?
As I've seen in the movies, could a .50 caliber round shoot down a fighter jet?

Probably even a .22 could with a lucky hit in the right place.

Possible duplicate of Can a fighter jet be hit by guns?

I remember also a question, which has an answer with this picture, but can find it now.

By .50 caliber, I believe you are referring to the .50 BMG cartridge.  The answer is yes, you could shoot down a jet fighter using such a round and plenty of jet fighters, such as MiG-15s, have been felled using that round during the Korean War.
In some respects the .50 BMG is a superior round to modern cannon rounds for shooting down jet fighters.  It's a small, fast round with good range, muzzle energy and penetration capability and can be fired at high rates, saturating sections of the sky with rounds, particularly useful for high off-angle snapshots in ACM.
In regards to penetration power, even a .22LR round could punch through the skin of a modern fighter.  The structure has to be kept light for weight and performance reasons.  Armor on fighters is almost unheard of, save for some plating on flight crew seats.  One exception to this is ground attack aircraft such as the A-10 or SU-25 which do have armor around the cockpit to protect the pilot at low levels.  The rest of the aircraft does not have armor and relies more on structural integrity and redundancy to protect the aircraft from ground fire.

not just BMG. The good old M1 HMG was and still is an effective weapon against low flying aircraft. As are .30 machine guns (though obviously they have shorter range).

Never heard of such a round.  There is the .50 Browning Machine Gun (12.7 x 99 mm NATO) originally developed for the Browning M2 heavy machine gun;

that's the one, the M2 HMG. I always get the M number wrong for that one for some reason... Of course there also is the older M1 (also called M1919 after the year of its introduction) Heavy Machine Gun, an older .30 weapon on which the M2 was based.


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What engine are these fan blades from?
I bought these from a metal scrapper and paid about $30.00 total figuring they're worth more than that in cool factor. Problem is they aren't nearly as cool if I can't figure out what engine (and hopefully aircraft) they come from. All I know is the compressor blade is titanium and the turbine blade has a high nickel content. So here I am hoping someone has an idea.
Also what might cause the wear patterns at the tip of the turbine blade? I appears like it may be cracked and then repaired. I cant imagine they would repair damage that extensive.
I cant find any pitting on the edges of either blade, leading me to believe neither blade was ever used, is my thinking correct?
Turbine blade

source album
Markings:
Suction side

1475M85  (Possible 1475M35)
BF P01 C (could potentially be a G at the end)

Pressure side

FDW157B9

TE

1435P02
59669 (hard to see, could be something else)
G12P

Compressor blade

source album
Markings
Foot:

B778503 FC
MOJR

It might not have even come from an aircraft engine either.

It may help if you include some measurements.

@LeonelArteaga Since the OP hasn't been on-line here in several years, I doubt he'll see your offer.  Since we don't really like to use SE as a classified advertising forum, I'm going to delete your post -- also because it includes your phone number, which may be unwise to have available like this to the world-wide internet.  It's possible to initiate a private chat room if you want to talk with a particular user, and that might be best in the future.

The compressor blades are Ti alloy, probably Ti-6Al-4V which is commonly used in fan and first couple of compressor rotor blades. It is genarrally better to not ask multiple questions in a single question. The damage and repair part should be a question on it's own. I can't answer it now as I need to duplicate a lot of information that is already answered on what part they are and from which engine. Note that it is scrap, it is not worth much, if new, you would be able to buy a car from selling a single turbine blade.

Turbine Blade
The turbine blade (part number 1475M35P01) is from the High Pressure Turbine (HPT) a CFM56-3 according to this ATSB report on performance testing of the engine. The report contains several images of blades which look similar to your photos.
Compressor blade
A search on locatory.com for the part number (B778503) lists the description as C-3 suggesting it could be a Stage 3 compressor blade. This would fit with the high aspect ratio of your blade.

The part number on the turbine blade shows it comes from a CFM56-3 series (Boeing 737 classic). No hits on the compressor blade, but it looks similar to one from the same engine.


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Why do fighter jets land faster than Jumbo commercial aircraft?
From my own understanding, the bigger (and heavier) aircraft, the higher approach speed it needs to keep itself from stalling. According to this site, the approach speed of an A380 is 140 knots, and 160 knots for a 747. In contrast, the F-16's landing speed is 141 knots, and 135 knots for the F-35C.
Doing mass-to-speed ratio, it doesn't make any sense to me. Could you explain why do fighter jets land faster while they are lighter than large commercial aircraft?

The landing speed is based on the "stall speed", which depends on the wing airfoil. A faster airfoil is not as efficient at low speed, and stall speed is usually higher. Concorde which had a faster airfoil also landed faster (155 kt), while this was a relatively light aircraft.

I'm not entirely sure you got the numbers right for your question, you have jumbo = 140-160 and fighter = 135-141 last I checked 135 is less than 140

@ratchetfreak , I am sorry if I get the number wrong. Could you provide the correct data, please?

Slow birds land slowly. Fast birds lands fast. Size has nothing to do with it.

This question could be improved by incorporating some consideration of wing loading.  If you really want to get fancy, talk about airfoils, and flaps.  But as has been pointed out, the average of 140 and 160 is greater than the average of 141 and 135, so this question defeats its own premise.

It is not only the mass that affects the landing speed. Wing area plays an important role as well.
A larger wing can lift more weight at the same speed than a smaller wing. If you compare the wing loading of these aircraft the differences are smaller:
A388:

Maximum landing weight: 391000 kg
Wing area: 845 m2
Wing loading: 463 kg/m2

B744:

Maximum landing weight: 295000 kg
Wing area: 525 m2
Wing loading: 468 kg/m2

F-16A:

Estimated landing weight: 13000 kg
Wing area: 28 m2
Wing loading: 464 kg/m2

I guess you mistyped B747 as B744.

Or, @sharptooth, he meant to use the shorthand for the 747-400

And, not just wing area, but wing size, shape, and AoA. Basically, what matters is the ratio of how much lift the wing produces at low speeds vs. the weight of the aircraft on landing. Aircraft wings that are efficient for supersonic flight are not efficient at low speeds and even subsonic wings are usually optimized for cruise flight speed. So, while a higher weight does mean a faster landing for the same airfoil, aircraft that are designed to fly faster will typically have faster landing speeds than slower aircraft regardless of how their weights compare.

For example, some of the newer 737s, if landing near their max landing weight, land faster than an A380 or a 747 typically would land. Here one of the posters mentions that he had recently landed a 737-900 with a final approach speed of 169 kts and was gaining on the 777 in front of him.

@reirab , how does cross wind affect landing speed?

@TBBT It's probably best if you ask that as a new question. It will get better answers that way and will be easier for people to find in the future (and better indexed by Google, etc.)

@FreeMan, that definitely makes a lot of sense (there are huge differences between B741, B742, B744 and B748), but then the first one should be A388!

@JanHudec You are right, I have updated the answer accordingly. The F-16A has designator F16, but so do other F-16 varieties. I leave that one as is.

Landing speed varies depending on several factors.
For airliners you have to take into account that the wing airfoil is radically different than the wing airfoil from a fighter jet: airliners have flaps that modifies the airfoil and doing so the lift and trail (not sure of this word in English) modifying the speed range of the wing (reducing the stall speed) and so allowing slower speed for landing.
In the case of a fighter jet the wing is in general a delta wing without flaps, so in order to reduce the speed for landing they have to increase the angle of attack to augment the trail without loosing too much lift. That why in this phase they cannot lower too much the engines and the speed, because their wings are not suited for low speeds. If you look at the Concorde (a good example of delta wing) they had to put down the nose during landing phase to be able to see the runway because of the high attack angle requested to be at the right speed (about 180-190 kt).

Fighters more often than not have flaps, just not the big multi-stage ones you see on big airliners. Take-off and landing speeds of these planes would be totally unworkable otherwise. They also typically have air brakes allowing the aircraft to approach under higher power, again without making landing speeds unworkably high.

The high angle of attack of Concorde is simply effect of using delta wing, which can naturally create lift at high angles of attack (vortex lift) and can't use flaps (they would act like elevators and pitch the aircraft down instead). The high landing speed reduced, not increased the angle of attack.

Because they are lighter, they have less kinetic energy so there is less to dissipate. This is easier on the brakes. Remember kinetic energy is $E_k=\frac{m \cdot v^2}{2}$.
Also fighter jets aren't as good gliders as jumbo jets. This sacrifices lift for maneuverability, so they have better acrobatic performance. While airliners will spend most of their airtime going straight ahead at high altitude so they benefit the most from being good gliders.

But the lighter plane having less kinetic energy isn't a reason for landing fast: it's a reason not to worry about landing fast. After all, if a light plane landed slower, it would have even less kinetic energy (since ke is proportional to the square of velocity), and be even easier on the brakes.

To simplify, the differences are similar to comparing a dart to a glider -- it all gets back to the wings.
The delta wing provides the best overall flight characteristics in terms of lift and control surface efficiency.  A delta wing will allow you to come in low and slow and in control, but is that always what you need if you are flying a fighter jet?
The aerodynamics of fighter jets are designed to provide lift, stability, and control at a much wider angle of attack.  Comparing the wing characteristics between the two planes in a wind tunnel, notice how the wing thickness (airfoil) of the fighter plane is much less (relatively flat) at the leading edge.
Although the fighter plane provides less lift at the same angle of attack and requires a faster airspeed to stay aloft without stalling, the control over a wider range of airspeeds is worth the tradeoff for the fighter jet performance and maneuverability.
Shut down a fighter plane engine, and it will drop like a yard dart.  The intake on a fighter plane is designed to receive as much air as possible, and will cause turbulence at the inlet if the blades are not turning fast enough.  There simply is a minimum speed range to keep the plane in flight and under control as it is coming in for a landing.
The power to weight issue has a downside -- the fighter plane is less efficient in fuel consumption -- it is even less efficient if the inlet has nacelles or ducting to mask a thermal signature.
The power to weight ratio of the fighter plane is much higher than a commercial aircraft, and the answers above from the other posters regarding thrust cover the topic well.
The best fighter jets provide the most maneuverability over the widest range of speeds.
Both types of aircraft would technically benefit from a lower landing (and stalling) speed, but in both cases, other flight characteristics are a higher priority.

Here's another factor in approach speeds - the military fighter/trainer aircraft I flew used 1.2 Vso (20% above landing configuration stall speed) for approach. Airliners are required to use 1.23 Vso and each model uses a different multiplier which often changes with different flap settings. The previous generation 727/757/767 mostly used 1.3 Vso while the newer airliners use 1.25-1.28 Vso.  That difference reduces a fighter's approach speed by 4-8% vs what an airliner would use.    Light airplanes use 1.3 Vso, or 30% above stall speed, for their approach speed.


text:
Can I wear a helmet camera in an open cockpit?
When flying an open-cockpit plane (specifically a Tiger Moth):

By Towpilot (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons
Where helmets are worn, what precautions or certifications need to be observed to mount a small video camera (such as a GoPro) thereto, if it's even possible? Obviously it would be very bad if the camera were to come undone in flight, and there might be an effect on the helmet's impact protection, so my guess would be that it's simply not allowed, but perhaps it can be done if certain conditions are met.

I guess the guy sitting behind you might have objections too, considering he'll be the first stop, should it come undone... ;)

Traditionally the student sits in the rear seat, which makes the empennage the first stop. I don't think that's any better on an aircraft made of wood and fabric. I'm assuming that you'd ask the instructor's permission as well as that of the airplane's owner or flying club, in any case.

Really? I always thought that the student was traditionally in the front seat? Hence the cut shirt tail

Well, Michael Schumacher has probably a word to say about the safety of such mounts.

It's certainly possible to use a GoPro in a Tiger Moth: there are plenty of videos online to prove it. That means the question is, is it legal and if so how to do it safely?
Legally, there isn't anything relevant that I could find on the UK's CAA site (your profile says you're in the UK), but in any case most discussions on cameras in GA aircraft have been about attaching a camera to the aircraft, not to the pilot (see this question, for example). For obvious reasons, it's difficult for any aviation authority to regulate what pilots wear or carry on their person and if there are no specific regulations that means that only the general don't do anything stupid or dangerous rule would apply. I assume that the UK has something equivalent to 14 CFR 91.13 in the US:

No person may operate an aircraft in a careless or reckless manner so
  as to endanger the life or property of another.

(Note: I'm ignoring any contractual issues here, like what your insurance company or FBO allows.)
From a safety point of view, the main risk of a portable camera is that it comes loose and ends up blocking a control surface externally (e.g. wedging in the rudder or elevators) or a control internally (e.g. falling to the floor and getting stuck behind a rudder pedal).
One specific concern with a helmet-mounted camera is that if it does fall off then it's very close to your face and it could obstruct your vision or even just startle you, which would probably be bad news on short final with a gusting crosswind. (Pilot distraction from operating the camera controls is another potential issue but that's true of any gadget.)
Ultimately I would say it comes down to how confident you are that the camera is secure and not going to get in your way: if you are, then go for it. I don't think the attachment issues are significantly different from skiing, parachuting, driving sports cars etc. with a helmet camera, and that happens all the time. And cameras are a great tool for reviewing and improving your performance (especially if you have full audio too), which makes the 'risk' very worthwhile, in my opinion.


text:
Is this ferry flight route possible for a B737-800 WL?
Recently a new aircraft, B737-86X (tail AP-BNA) was delivered to a new airline in Pakistan.
The ferry flight as reported by planespotters is BFI - BGO - KHI but this seems like a large stretch given the performance of the aircraft (range of 3,115 nm); so I am trying to find the exact ferry route taken.
However, flightware only shows the test flight when I search by the tail number.
Is there a way to find out what the actual flight plan was?
To clarify based on comments:
I am aware that additional modifications can be done on ferry flights (since these are not normal passenger flights) - such as adding of additional fuel tanks - however, due to the facilities available at KHI I doubt this was the case.
Further I understand that it may be possible that the plane was flown BFI-BGO-KHI - even without any further modifications (favorable winds, etc); so I am trying to find a way to confirm what was the actual flight plan; or if crew-only 737-8 WL can fly that route without modifications.

Its possible the performance of the empty aircraft allows such a flight to be made or its more than possible they installed ferry tanks

Looking at the map makes me wonder: since it's a ferry flight, there aren't any passengers to get upset by an extra stop. Can you take of with Norway as intended destination, but with officially insufficient fuel, using Iceland as an extra stop if the Jetstream is unfavourable? Or the other way around, have Iceland as the planned stop, and if the Jetstream is favourable, replan to Norway?

related: How do airliners get from the factory to the client if the aircraft does not have the required range?

Just to clarify, I am not asking how to retrofit the aircraft to make that flight, I am asking if there is a way to validate if BFI - BGO - KHI was the actual route taken.

@BurhanKhalid You may edit your question to add this clarification in it.

As @Dave said, 3,115 nm  is the range fully loaded (full of passengers and baggage).
As a relocation flight, it almost certainly had no passengers and minimal crew.  Its range would be considerably greater.
It may also have extra temporary fuel tanks installed, if needed.

I understand that on some flights, ferry tanks are installed. But as there are no facilities at KHI to do a complete interior of the aircraft; I doubt this was the case.

An empty 737-800, correctly configured, would have no trouble whatsoever with the 3800+nm longest leg on this flight, actually -- using the 737 airport planning document's payload-range chart for the 737-800 on PDF page 96, and assuming that it has at least one fuel capacity option installed (the base model with no body tanks can't make the trip for fuel capacity reasons), we get a maximum range for 100klbs of OEW+payload (i.e. over 4 tons of payload margin available) of a bit over 3900nm, and over 4000nm range for the no-payload case (91.3klb representative OEW).  Of course, if the plane has more fuel tanks installed, it can fly further as it's fuel capacity limited at such light payload weights.

@ymb1 That requires the airline to order the full complement of aux tanks though.


text:
Is there's any risk using modern C++ compiler on DAL A Display Application Flight Software?
I am C++ enthusiast and I like to design and architecture my software with latest C++ features specially with templates,  but I have been struggling hard to find a way.
The compiler we use for LynxOS-DO178 RTOS with PowerPC architecture is more than decade old, with poor optimization, lack of several features, and often times just ending up in "internal compiler error". Code bloating occurs with simple template instantiations, which could be easily remove with latest compilers.
All ideas and innovative improvements are simply stopped by the fact that our compiler cannot support this and that.
I believe I could get a tool chain for my cross-platform development supporting somewhat latest versions of GNU GCC/G++. But not sure if that can be ever certified for DAL A SW.
We have now C++14, approaching to C++17, still I have this question do we have anything modern yet from C++ that sees "light of sun" on a critical SW ?
What are the risks, cons, etc for a flight critical SW ?
Bjarne Stroustrup recently announced core C++ guidelines, that resolves around use of modern C++11/14 and templates, but can we ever use those on Flight DAL A SW ?
Not sure if this a right platform to discuss this, if someone knows a better platform please direct me to that.

Posed a bit more generally, this might get a better reception over at ProgrammersSE.

Can any moderator help me to move this at Programmer Stack Exchange ? Or may be somebody should vote for moving it. Thanks

I think the question is relevant to the site. It's not just about how to encourage a business to move to new tools: it's specifically about certification requirements for aviation software.

@DanHulme but for that we already have questions: http://aviation.stackexchange.com/q/19347/1467 http://aviation.stackexchange.com/q/3406/1467 http://aviation.stackexchange.com/q/3405/1467

@Federico Exactly, there's a history of similar questions about software certification being on-topic on this site. This one is just more specific than those questions.

Thanks for the answer/comments,  but I'm interested in knowing more why till date no one has ever  thought about use of
modern C++, is there any risk involved. Or may even any of organization already use advance C++ features ?
What are the ramifications ? I need some moderator help to tell me where to post this, I already flagged for moderator attention

For one thing, the use of modern anything in the aviation industry is rare to unheard of. Not to mention bleeding edge like you are talking about. Change upsets the system, and even though a technology may have clear benefits the industry is so risk-adverse that the status-quo takes a lot to upset, and when it does it takes years of testing (and perhaps dealing with applicable regulations) until it reaches production status and sees actual use. In general "more than a decade old" is still the front-end of a lifespan. Perhaps not exactly so for software but you get the idea.

Really late, but I don´t think there's a problem with C++17 as long as you test everything. But things like templates increases tests complexity, you have to test every possible instances and things like that. I bet testing template metaprogramming can become a pain.


text:
Why are ambient pressure and burner can pressure always the inputs on a hydromechanical fuel controlling system?
I worked on several of these older systems using a hydromechanical fuel control. I've noticed that the inputs at the fuel control are for the most part the same. Power lever angle, N2(N1 on a single spool), ambient pressure (usually Pamb or whatever the manufacturer calls it), and burner pressure (sometimes Pb4, again depends on manufacturer). My question specifically pertains to the pressures.
Why is it always ambient pressure and burner can pressure that are inputs? Why not compressor discharge pressure and turbine exhaust pressure or some combination of other pressures in the engine?

Note that pressure only very gently decreases over the hot section, so there is not much difference between compressor discharge pressure and burner pressure.

Hydromechanical Fuel Control Units (FCUs) typically do use compressor discharge air pressure as an input.
As I recall, the FCUs that I am familiar with have had at least the following inputs in addition to the control lever commands:

Compressor Rotation Speed
Compressor Discharge Air Pressure
Ambient Air Pressure

As both a mechanic and pilot I have studied many FCUs, and I do believe the inputs listed above are standard across all those with which I am familiar. This is certainly true of the types that I have studied most recently and the systems which I currently fly. Note that while these FCUs may be older designs—in some cases—they are commonly used on new production turbines.
The following are excerpts from some of my training manuals concerning a Bendix FCU:

The pneumatic section of the FCU determines
  the flow rate of fuel to the engine for all operations.
  The power levers control engine
  power from idle through takeoff power by operation
  of the gas generator (N1) governor in
  the FCU. Increasing N1 rpm results in increased
  engine power.
For explanation purposes, consider the N1 governor
  bellows as a diaphragm. P3 air is introduced
  into the bellows in a manner that sets up
  a differential pressure on each side of the diaphragm.
  Therefore, any change in P3 pressure
  will move the diaphragm. When pressure
  is increased, the fuel-metering valve attached
  to the bellows will move in an opening direction
  to increase fuel flow and increase N1 rpm.
As P3 pressure decreases, fuel flow also decreases
  which reduces the N1 rpm. The N1
  governor increases or decreases P3 pressure in
  the bellows by varying the opening of relief
  orifices in the bellows.
The FCU controls engine power by maintaining
  the requested N1 rpm through the N1 governor.
  If actual N1 rpm is lower than the desired
  setting, the N1 governor closes the P3 orifice,
  allowing pressure to increase. As the pressure
  increases, the diaphragm moves to open the
  metering valve, increasing fuel flow, which in
  turn increases N1 rpm to the speed requested by
  the governor. When N1 rpm reaches the desired
  speed, the governor adjusts the P3 orifice to reduce
  pneumatic pressure to match the fuel pressure
  required to maintain the desired N1 rpm.

That's informative and I appreciate the information, but still, why do most fuel controlling systems use ambient and burner can pressures? What is so important about burner can pressure?


text:
Is there a real temperature change along a streamline when its velocity changes?
Stagnation enthalpies are given as
$H_T=H+\frac{v^2}{2}\ $
Along an adiabatic inviscid steady flow streamline Stagnation Enthalpies are said to be constant.
$H_{T1}=H_{T2}$
$H_1+\frac{{v_1}^2}{2}\ =H_2+\frac{{v_2}^2}{2}\ $
$H_1-H_2=\frac{{v_1}^2}{2}\ - \frac{{v_2}^2}{2}\ $
$H_1-H_2=\frac{{v_1}^2-{v_2}^2}{2}\ $
Stagnation temperatures are  also constant
$T_0=T_1+ \frac{{v_1^2}}{2CP}$
$T_0=T_2+ \frac{{v_2}^2}{2CP}$
$T_1+ \frac{{v_1}^2}{2CP}=T_2+ \frac{{v_2}^2}{2CP}$
$T_1-T_2= \frac{{v_1}^2}{2CP}- \frac{{v_2}^2}{2CP}$
$T_1-T_2= \frac{{v_1}^2-{v_2}^2}{2CP}$
In both of these equations there is derived a notion of a static enthalpy and static temperature at a point of interest along a streamline. These can be different by the value of the flow velocity v
This is stated to be applicable to compressible and incompressible flow
Is it correct to say that there is a real temperature change $T_1-T_2$ along a streamline when its velocity changes?

Don't know what you mean by real temperature. You will certainly experience a change of static temperature in an adiabatic flow if the velocity changes.
Stagnation enthalpy describes the total energy contained in the fluid which comprises inner (thermal) energy, kinetic energy (and potential energy which is often neglected). Stagnation enthalpy is constant for an adiabatic flow with no energy exchange. Thus, thermal and kinetic energy are antagonistic in the sense that increases of the kinetic energy need to be countered by reducing thermal energy in order to keep a constant value of total i.e. stagnation enthalpy, and vice versa.
The stagnation temperature of a fluid is a virtual entity, temperature entities that are observable i.e. measurable are static temperatures. However, in a stagnating point the static temperature ideally features the value of the stagnation temperature.
Back to your question: If you measure temperatures in an adiabatic flow at points of different flow velocities, you will experience different temperature readings. Your measurement setup has to ensure that your readings are not falsified by slowing down the fluid at the points of measurement.

Thanks for your reply Chris that’s exactly what I would expect but I also keep getting referred by some very smart people to the work/energy theorem (applied to Bernoullis incompressible adiabatic) saying that $dU=dQ+dW =0$ and therefore if $dU=0$, $dT=0$.
This does not account for the conversion along a streamline of  Static enthalpy $H$ to Dynamic enthalpy $v$ , which as you say for constant total enthalpy $H_T$ must mean a reduction in Static enthalpy $H$ If $PdV=0$  this must come from static $U$ which explains how the temperature changes with no $dQ$ or $P.dV$ Which one is right ?

U is for closed systems, H describes open systems as you regard it. Both entities are linked via H = U + pdV.

Hi Chris thanks for your reply , I don't understand the open and closed distinction, researching it seems both energy balances can have a change in the kinetic term while $dQ$ and $P.dV$ are zero


text:
Is it possible to build a paper airplane that will enter a fully developed spin?
Some students learn best when they can see aerodynamic principles in action. I'd really like to be able to show a student how a spin occurs.
Is there a way to make a paper airplane that will enter a developed spin?

Awesome question. I'd guess it should be possible, but perhaps not easy. It needs to have just the right amount of pitch authority to keep the wing "stalled" without pulling it into tight loops. It also needs a center of mass slightly forward of the center of lift so that it pitches down in a stall. Then theoretically all you need is a little roll/yaw input (make a flap on the vertical fin). Are you good with paper airplanes? I'm not :) Looking forward to some real answers!

(That said, I am such a student... but I think it would be just fine for an instructor to show me by holding the paper (or model) airplane and talking through the steps slowly, moving the airplane through the motions. This would be really cool for its own sake, but maybe not strictly necessary for educational illustration. The paper airplane is going to move pretty fast, and it will be hard to "see" the crucial concept that the wing(s) are stalled due to high AoA and one wing is stalled "more" than the other.)

Balsa wood is probably better than paper.

Possibly irrelevant but Towards Disposable Low-Cost Folded Cellulose-Substrate UAVs has some discussion of flight modes in section 3.3.

@DJClayworth RC aircraft would be even better to show such thing, but paper is cheaper and easier to carry inside a teacher's bag (e.g. inside a book)

Besides the location of the center of gravity, two things determine how an aircraft spins, and both are not well shaped for spinning in paper airplanes:

The wings (obviously): They should ideally be straight with an aspect ratio between 5 and 10. Swept wings will also spin, but straight wings make spinning and recovery easier.
The forward fuselage. Here a rounded shape which is higher than wide is ideal and will promote flat spins. The two-dimensional shape of paper airplanes will not produce the vortices which drive the yaw rate in spins.

Also, for spinning it needs a stalled wing, some asymmetry and some time until the spin fully develops. To create a strong pitch-up moment, masses at the tip and the end of the fuselage are also needed. A pure paper airplane will have too much yaw damping and too little inertial pitch up to spin.
Size should be less of an issue because separated flow changes less with Reynolds Number, and spin tunnels regularly use scales of 1:20 or 1:30 with good results. But I wonder whether the low wing loading of a paper airplane will prevent spins - the models used in spin tunnels are carefully sized not only for geometric agreement, but also for their masses and mass distribution.
Maybe it will be better to show your students videos from spin tunnel tests.

Spin tunnel footage of fighter aircraft
Spin tunnel footage of GA aircraft
Description of a spin tunnel

Your video link died, so I took the liberty of inserting a new one. I don't know if it reflects your intended meaning, however, so please have a look.

@AEheresupportsMonica: Many thanks for keeping the answer up to date! I added a few more links, hoping that at least one will survive for some time.

Excellent videos.  Rudder position (acting as vertical airfoil) seem to affect spin to a greater degree than weight asymmetry (and fuselage too).

I don't know if this will work for you, but I used to put little tears towards the body on the leading edge of the paper airplanes I made.  Then I'd bend the leading edge of the wing down a bit to create a stronger airfoil.  I'd do this simply to increase lift at low speed, kind of like slats.  But I wonder, if you put a tear on only one side and adjusted it properly, perhaps you could make it so that one wing stalls out before the other?
Or, perhaps to be a bit more accurate, you could just go with tears on both sides but adjust one down further than the other.  That way it's pretty apparent that on wing is developing more lift at low speed.

If one can handle a little abstraction, a half maple leaf seed is perfect.
The main driver of an established spin is lift and drag asymmetry, resulting in a helical spiral downwards.  While fuselage shape and weight distribution are contributing, difference in lift between the two wings results in a slip towards the lower lifting wing.
Once the aircraft starts to slip, the center of drag will determine the the torquing force around the center of gravity.  It is here that yaw force is created.  The higher drag of the inside wing "locks" the lift asymmetry.  Combined with loss of forward speed and stall, the aircraft drops "like a maple seed".
By applying opposite rudder, the pilot stops rotation and "brings the other wing of the maple seed back", which equalizes lift and drag on both sides.  The aircraft can then regain airspeed and reduce angle of attack by pitching down.
So, for a small model, a paper clip or some type of weight on one of the wings will do it, along with a lack of wing dihedral.  A paper airplane will be more difficult as its larger surface area to weight ratio tends to slow rotation.

One can create drag asymmetry by stalling one wing or with rudder into spin.  A sufficient amount, along with lift asymmetry, will cause the "aircraft" to spin.  On this particular model, even though the swept leading edge was trying to stabilize to with its "dihedral effect", the destabilizing forces of the rudder and offset of center of lift and center of gravity spun it well.


text:
How much force is produced by control surfaces?
Context:
For some context, I'm a game developer and I'm building a flight sim game. My goal is to have realistic -- not arcade -- physics. The game is in Unity. Unity handles the actual application of the forces -- I just calculate the numbers.
The forces applied to the plane are:

$F_T = \text{Thrust}$ applied to both engines directed forward relative to the plane
$F_L = \text{Lift}$ applied to the center of lift directed perpendicular to velocity
$F_{RR} = \text{Rolling Resistance}$ applied to the center of mass and directed opposite to velocity
$F_W = \text{Weight}$ applied down at the center of mass
$F_{AR} = \text{Air Resistance}$ applied to the center of mass and directed opposite to velocity

The center of mass is positioned slightly forward of the rear landing gear. The center of lift is slightly behind and above the center of mass.
I use a constant thrust directed forward relative to the plane, a constant weight force directed down (world), lift calculated with the below equations directed perpendicular to velocity, and drag directed opposite to velocity. I also have a down force provided by the elevators.
My plane is loosely based on an A320 using a wide variety of figures found online. The mass is $72,000 kg$, wing span is about $35m$, wing area is about $122m$, engine thrust is $110,000N$ each, rolling friction coefficient is $0.04$. The lift coefficient is taken from a table graphed against angle of attack. It looks something like the Cessna graph shown here. The drag coefficient is calculated based on the lift coefficient (formula shown here).
Here is a screenshot of the plane and the forces. Pretent it's an A320 -- it's just a placeholder for now. At the time of the screenshot the plane was travelling at $150kn$.

Issue:
When I apply full throttle to the engines, the plane accelerates as normal. However, upon reaching a typical airliner rotation speed of $150kn$, precisely nothing happens. The plane doesn't lift off the ground until reaching almost $300kn$ where $F_L$ finally overcomes $F_W$. The way I see it, there are two possible causes. First is that my lift maths is wrong, and second is the force provided by the elevators is wrong. I calculated lift as shown here in my other question.
This begs the question, how much force do the control surfaces provide? In particular, the elevators. I know the horizontal stabilizer acts essentially as an upside down wing where the elevators act like flaps/spoilers. I tried using the same lift equation but the force was much to high and the plane would spin uncontrollably on the spot. I also tried calculating (estimating) by hand the torque required to overcome the torque lift of the wing due to the center of lift being behind the center of mass, and then a bit extra to make the torques unbalanced causing rotation. However this was not enough force.
Similarly, how do I calculate how much force is provided by the ailerons, flaps and spoilers -- how do I model this mathematically? Does it just modify the coefficients of lift/drag or do I apply a whole new force?

How much fidelity do you want to get? Seems like you are treating the airplane as a point mass, so you are missing the three rotational degrees of freedom.

Well that's the thing. I'm only treating it as a point mass by applying forces to the COM because I don't know where else to put them...

It sounds like you are trying to develop something similar to FSX, which models based on force values and axis locations etc etc.  Xplane does it a completely different way, by calculating the aerodynamic forces on each square inch of the entire body and deriving behaviour from that.  Xplane is considered a much more true to life simulation and is used by ultralight and light sport manufacturers as a "poor man's wind tunnel".

@JohnK Interesting! Where might I find the maths related to this? I'm not really sure what to search for.

Try Xplane coding or Xplane modeling, Xplane development, or something like that.  Just plug various words behind Xplane.  You will probably stumble into a developer forum or some such eventually.

I'll give that a try. Thanks for the suggestion!

I suggest that you take a look at jsbsim http://jsbsim.sourceforge.net/download.html It is opensource and can model aircraft dynamics.  There is even an a320 model that you can start with: https://github.com/JSBSim-Team/jsbsim/tree/master/aircraft/A320.  It is also the primary flight dynamics model behind the https://www.flightgear.org/ and opensource flight simulator.

@Adam Although it looks very good, this is in cpp and would be a real pain to implement in Unity. I tried reading through the source code but I just don't understand it.

@mr-matt I suggest that you can use the jsbsim executable to calculate some sample forces.  As far as integrating them, it looks like it has been done before:  https://forum.unity.com/threads/jsbsim-flightgear-engine-with-unity.248658/

From the OP, it seems like you are treating the aircraft as a point mass. As a point mass, you don't get the rotational degrees of freedom, so control surface can't be accurately modeled. In the case of takeoff, rotation is achieved via elevator up force, resulting in aircraft pitching up, increasing its angle of attack, resulting in increased the overall lift and achieving the initial vertical acceleration. In summary, you can't model it from first principle without the rotational degrees of freedom.
There are a few things you can do.

You can continue to assume point mass. You can assume some simplified parametric model for takeoff rotation. That is, the trajectory is a parametric relationship of airspeed, time and elevator. It's not a physical model and it won't be accurate to the magnitude of elevator application, but it may suffice. Once in the air, you can do the same thing with banked turn for aileron applications, and airspeed changes with elevator. Essentially, you are working with a performance model (see performance equations of motions), with artificial relationships for control surfaces.
The above may suffice if all you want to do is GTA style flying (as an aside, its takeoff behavior is terrible). It'll look like a plane flying, but won't feel like a plane flying to anyone who's flown a plane.

You can move up to six degrees of freedom. In that case, you'd need more than just lift, drag and thrust; you'll need moment relationships as well. I recommend you to give Etkins, Dynamics of Flight a read. You can skip directly to Chapter 4. You'd be in very good hands once you've read Chapter 4 and 5.

"Etkins, Dynamics of Flight" This looks very good. I'll have a read!


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How do I calculate the center of lift?
See my other question here for the background context.
Consider this simple plane. I have applied the 4 basic forces: lift, drag, weight, and thrust. My question is, where, precisely, do I apply the lift force?

I've read through this which says it's at a quarter of the chord length. But where does that sit in 3 dimensional space? Most airliners have slightly swept wings. The chord length also changes along the wing. How can I model this mathematically?

Center of lift changes with angle of attack. It's not that useful for aeronautics or modeling.

Related: https://aviation.stackexchange.com/a/48212/34686 ; search the term "Center of Pressure" on ASE for more.

The Centre of Lift (CoL) of the whole aeroplane is a summation of the lift forces of the wing, the fuselage and the horizontal stabiliser. The wing has the largest contribution to the lift of course.

Above figure is from Torenbeek, Synthesis of Subsonic Airplane Design, and shows how to construct the Mean Aerodynamic Chord of a swept wing. The CoL of a subsonic wing is taken at 25% of the MAC in the pre-design phase - this answer provides some more detailed information.

Above pic from this answer shows the relation between CoL, Centre of Gravity and tailplane lift/downforce: it is an equation of moments about the CoG.
The arrow at dC$_{NW}$ is the wing lift, dC$_N$ the composed aeroplane lift, and at dC$_{Nh}$ the tailplane lift. Which can be positive in cruise, however at take-off the stabiliser will need to generate a downforce, shifting the aeroplane lift balance point forwards (the wing lift can still be assumed to be at 25% MAC in this stage of your design).
If CoL of the complete plane is in front of the CoG, the nose of the aeroplane will tilt up.

In the air, in steady state flight at a given airspeed, the 4 forces of flight are in balance.  Therefor, it might be easier to work this backwards.

for zero pitching moment the center of all lifting forces are directly at the center of gravity

This includes lift contributions from all parts of the airplane and the thrust vector.  From your modeling, start with the wing and tail.  The clue is "elevator force ON".
The key is to find the Cm plot of the wing you are using.  Starting with your straight "candy bar" wing design, pick an airfoil to determine elevator force required for a given center of gravity location.  Cm tells you about the stability of the wing itself at various angles of attack by comparing center of pressure to the aerodynamic center, and is stable in negative values. It may vary with AoA.

pitching moments of the wing center of pressure relative to the center of gravity must be balanced with the elevator.

Location of center of gravity will become important later on as you model pitch stability.  In other words, do you want your aircraft to require computer control like a fighter jet or to be rock stable like a cargo plane.

My question is, where, precisely, do I apply the lift force?
I've read through this[3] which says it's at a quarter of the chord
length.

The idea of the lift force acting at the quarter-chord point 1) is only a convention and 2) is only valid if you also specify an aerodynamic pitching moment, which compensates for where the lift force is actuallyeffectively acting.
An exception is the case of fully symmetrical airfoil (i.e. an airfoil with no camber), in which case the lift force does act very near the quarter-chord point, with no additional aerodynamic pitching moment to consider.
If the plane you are modelling has a cambered airfoil, then you can't pick a single point where the lift force effectively acts.  The Center of Lift moves forward as angle-of-attack increases, and moves aft as angle-of-attack decreases.  This destabilizing effect is the reason that most aircraft need tails.


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What would happen if put a jet engine behind another jet engine?
Just curious. Would it do nothing, would it generate a massive amount of thrust? Would it even work?

They're called afterburners.

Really?! So is that what a fighter jet uses?

@BillOer No they are not.  Simply put, afterburners inject fuel into the hot exhaust.

@MatthewInglis A jet engine needs cool, unburnt air to suck in.  The second engine simply wouldn't work.  Sometimes, engines have stopped because they've sucked in exhaust from another engine meters way.  One behind the other will never work.

@Simon, simply put, an afterburner is a ramjet engine behind a turbojet engine that (as you correctly point out) injects fresh fuel into the ramjet.

Ah that's interesting, thanks guys for clearing that up

https://en.wikipedia.org/wiki/Afterburner

@BillOer An afterburner is not a ramjet.  There is no compression.  A ramjet also needs clean, unburnt air just the same as a jet engine.  The only difference, at the most basic level, is that in a ramjet, compression is achieved through the forward motion of the engine rather than by using rotating compressor stages.  A ramjet behind a jet engine will fail in just the same way.

You can use a jet to start another jet by using the thrust from the jet in front to spin up the one behind. The USAF used this technique in the 50s and 60s, and may still use it today.

@GdD As I remember, in the late 1980s or early 1990s when I was flying for Evergreen Airlines, one of our DC-8s was intercepted and forced to land in Iraq. When it was allowed to leave, there was no compatible equipment equipment with which to start it, so they backed up one of their fighters to one of the DC-8's engines and did it that way.

@GdD, we used to use turbines to start turbojets in the Corps in the early '70's. I actually burned my hands on the cowling of one. I believe the A4s needed turbines. This was a very long time ago when I was doing Visiting Aircraft Line at MCAS El Toro. Later they finally put me in Avionics where I was supposed to be.

If you want a very good example of what ingestion of hot gasses can lead to, the Boeing X-32 suffered from this issue during its development - during the hover phase, it started ingesting hot gasses from its own engine, leading to a issue called a "pop stall" - you can see it in action at the end of this video (the last 20 seconds or so) https://www.youtube.com/watch?v=16EdXpk2SkU

There is an alternate way to answer your question, and it relates to thermodynamics.
Think about the purpose of a jet engine.  It exists to take uncompressed air, compress it, mix it with fuel, burn it efficiently and then expand it (hopefully adiabatically) to generate a larger volume of gas at higher pressure than the intake.  The work done by the engine is described by the Brayton cycle (Figure 3.13 from http://web.mit.edu/16.unified/www/FALL/thermodynamics/notes/node28.html), and this cycle shows us where we can and can't hope to achieve theoretically efficient operation.
If you look at the chart of the cycle in the above reference, you'll note that the compression and exhaustion portions of the cycle are where inefficiency (in the form of entropy) creep in and prevent the cycle from being perfect.  As such, even if there were sufficient oxygen left to burn, putting two jet engines back to back would be horribly inefficient (because you are repeating the inefficient portions of each twice).
The better solution is to work towards improving compression ratios, and recovering more work from expansion.  Much of this has been done over the last 50 years, and is why Brayton efficiencies are in the 0.6 to 0.7 range for modern jet engines (ref same website, Figure 3.19).
EDIT: Also, remember that jet engines are designed to work on air that is "cold" relative to their exhaust. They don't compress hot gases efficiently. You could certainly design a compressor to efficiently compress hot gases for combustion, but jet engine compressor sections are not designed for this, so the compression achieved by the second engine in your question would be MUCH lower than its design, which would further decrease it's contribution of additional thrust.

Engines need oxygen for fuel combustion.
Turbojet
After most of the oxygen has been extracted and used to oxidize / burn fuel in the first engine, air is no more useful. In the second engine the core combustion wouldn't start, air would just turn the discs, but there would be no compression, so no additional thrust (discs would actually slow the flow).
Afterburners try to burn the remaining oxygen after the core combustion, but there is only the previously mentioned limited quantity to burn. An afterburner is not a second engine, it has no rotating parts, only burners.
Turbofan
In addition of the core flow, a turbofan has a bypass flow. The bypass flow is not used for combustion and still contains its oxygen.
However this flow generates most of the thrust by air compression / acceleration, so anything which slows the cold flow also degrades the engine efficiency.
There is a technique to burn the bypass flow: The plenum chamber, but this requires something different and no rotors are involved.

Your statement that O2 is required enter directly in contradiction with this answer http://aviation.stackexchange.com/questions/10034/if-jets-carried-pure-o2-to-use-for-combustion-would-they-be-more-efficient

I think there's more oxygen than you might think coming out of a turbojet tailpipe. Wikipedia says, "Less than 25% of the air is typically used for combustion, as an overall lean mixture is required to keep within the turbine temperature limits." https://en.wikipedia.org/wiki/Turbojet#Combustion_chamber

@FredLarson: I can't find a detailed analysis of the gas showing the exact amount of O2 remaining. Do you have one? Wikipedia wording is ambiguous (air vs O2, core vs core+bypass).

No, I'm afraid I don't.

Your question was inadvertently answered by Peter Kämpf when he provided this answer to another question.
One jet engine was placed in front of another in a test facility to test the high speed, high altitude performance of the trailing PW J58 when it was chosen to power the SR-71. Test details located here.

You would end up with an extremely inefficient setup, if it works at all. It's not the lack of oxygen, because only 20-25% of the oxygen is begin burnt in the core jet engine, so there should be plenty of oxygen left for the second engine.
The high outlet temperature of the first engine would decrease the power of the second engine dramatically. The exhaust velocity of ENG1 would be reduced by ENG2 as it wouldn't be able to process the incoming volume of air. The turbulent flow will reduce the compressors efficiency as well.
All in all, there would be no benefit to such a setup at all.


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If a shoulder harness becomes INOP in an aircraft certified before 1978, is it still required equipment?
So we fly a 1973 Piper Archer, with shoulder harnesses installed from the factory. The question is:
Would the shoulder harness becoming INOP (jamming & not coming loose) ground this airplane or could you fly without it, since the FAA required shoulder harnesses as of 1978 (or some other year...?)?

Shoulder harnesses have been required for all aircraft manufactured since December 12, 1986 for all seats, July 19, 1978 for front seats.
14 CFR 91.107 (2) and (3) is pretty clear:

(2) No pilot may cause to be moved on the surface, take off, or land a U.S.-registered civil aircraft (except a free balloon that incorporates a basket or gondola, or an airship type certificated before November 2, 1987) unless the pilot in command of that aircraft ensures that each person on board has been notified to fasten his or her safety belt and, if installed, his or her shoulder harness.
(3) Except as provided in this paragraph, each person on board a U.S.-registered civil aircraft (except a free balloon that incorporates a basket or gondola or an airship type certificated before November 2, 1987) must occupy an approved seat or berth with a safety belt and, if installed, shoulder harness, properly secured about him or her during movement on the surface, takeoff, and landing.

So what I read above can be interpreted as "if it's installed, it's required".
Some aircraft required an STC to retrofit the belts, you'll need to find out if that is the case (if it is, you can't remove it, but if there is no STC it could possibly be removed, a call to your local FSDO can clear that up). However I've been told that if the aircraft is equipped with shoulder harnesses, then they are required to be used.

You wouldn't necessarily need an STC, you could just do a 337 for an alteration. Either way, maintenance work would probably be required beyond the capabilities of a non-mechanic pilot.

@JonathanWalters As far as I've read,  originally the FAA was requiring STCs but stopped that so they could be retrofitted with less certification. Some aircraft as a result may be modified under an STC.

FAR 91.105 also applies - specifically paragraph B, subparagraph 2 which says you don't have to wear the shoulder harness if it interferes with performing your crewmember duties (an inop shoulder harness that doesn't let you move to reach all of the controls would prevent you from performing your duties). That would then fall to 91.213 like Steve mentions. All that said, it'd be dumb not to get it fixed before flying. Shoulder harnesses save lives!

@voretaq7 I'm not sure the spirit of 91.105 (B)(2) means you can inop a shoulder harness and say it interferes with your duties. I think it allows you to undo your shoulder harness to reach critical controls that may be out of reach, like breakers or other things... 91.105 also says you can get out of your seat if it is required to perform your duties, but under the same line of thought, you can't say an inop seat "interferes with duties" and pilot on the floor with an inop seat...

@RonBeyer I would also agree that it isn't in the spirit of the regulation, and I imagine the FAA would take a dim view of an argument based on it. The only case I can see for it applying at all would be a harness stuck (or more likely locked by a maintenance action) in partially extended position such that it could be worn for some portion of the flight, but would have to be removed for others. Of course if you're performing maintenance to freeze the inertia reel so it acts as a fixed strap there'd be no reason not to fix the stupid thing properly...

I might put this in the answer but it's also important to note that the belts aren't there just to keep you safe in a crash,  more importantly they are there to keep you in your seat, during things like unusual attitudes and turbulence,  both of which usually happen unexpectedly. If you can't reach the controls, you can't control the aircraft...

You're good to go... most likely:
There are decisions based on FAR 91.213 (d) that would have to be answered first but if you run down those, odds are favorable that you will find that you can legally de-activate or remove the shoulder harness in an airworthy manner.
To be considered airworthy your aircraft must meet its FAA approved type design or be in a properly altered state. That means everything installed must work or be altered "properly".
So how would you "properly" alter your Piper with the shoulder harness issue?
FAR 91.213 (d) allows you to fly with inoperative instruments or equipment.

(d) Except for operations conducted in accordance with paragraph (a)
  or (c) of this section, a person may takeoff an aircraft in operations
  conducted under this part with inoperative instruments and equipment
  without an approved Minimum Equipment List provided—
(1) The flight operation is conducted in a—
(i) Rotorcraft, non-turbine-powered airplane, glider, lighter-than-air
  aircraft, powered parachute, or weight-shift-control aircraft, for
  which a master minimum equipment list has not been developed; or
(ii) Small rotorcraft, nonturbine-powered small airplane, glider, or
  lighter-than-air aircraft for which a Master Minimum Equipment List
  has been developed; and

OK, your piper clears #1.

(2) The inoperative instruments and equipment are not—
(i) Part of the VFR-day type certification instruments and equipment
  prescribed in the applicable airworthiness regulations under which the
  aircraft was type certificated;

Your Piper was certificated under CAR3... just try to find anything about shoulder harnesses there...  So far so good...

(ii) Indicated as required on the aircraft's equipment list, or on the
  Kinds of Operations Equipment List for the kind of flight operation
  being conducted;

Read through your AFM or POH to see if it requires it. Maybe it does but I doubt it.

(iii) Required by §91.205 or any other rule of this part for the
  specific kind of flight operation being conducted; or

91.205 requires lap belt only (metal type) but does not mention shoulder harness. I'm assuming the shoulder harness is not an integral part of the lap belt. This is key... you need a lap belt.

(iv) Required to be operational by an airworthiness directive; and

Been doing this my whole career and I'm not aware of an AD about it that is applicable to your aircraft.

(3) The inoperative instruments and equipment are—
(i) Removed from the aircraft, the cockpit control placarded, and the
  maintenance recorded in accordance with §43.9 of this chapter; or
(ii) Deactivated and placarded “Inoperative.” If deactivation of the
  inoperative instrument or equipment involves maintenance, it must be
  accomplished and recorded in accordance with part 43 of this chapter;
  and

Ok, you need to have an A&P remove or deactivate it, write a maintenance entry about removing it and placard it as "inop" if necessary.

(4) A determination is made by a pilot, who is certificated and
  appropriately rated under part 61 of this chapter, or by a person, who
  is certificated and appropriately rated to perform maintenance on the
  aircraft, that the inoperative instrument or equipment does not
  constitute a hazard to the aircraft.

Well, it could constitute a risk to the occupant I suppose, but not a hazard to the aircraft.

An aircraft with inoperative instruments or equipment as provided in
  paragraph (d) of this section is considered to be in a properly
  altered condition acceptable to the Administrator.

That's how you properly alter your shoulder harness issue to a manner acceptable to the FAA...

An argument could be made under sub-paragraph 4 that if you get bounced around and hit your head on the panel you could be knocked out, and that would then pose a hazard to the aircraft as the PIC would be incapacitated -- Of course the case could also be made that conditions rendering that likely would also be a hazard to the aircraft, and raise questions about how you encountered such conditions.